Influence of wet-dry cycles on the temporal infiltration dynamic in temperate rice paddies

• The infiltration rate decreased between the first and second cycles.
• The infiltration rate reached its maximum value at the growing season end.
• Large amount of water infiltrated during the first 40 h of each wet-dry cycle.
• One-month delay irrigation did not save water.

Rice paddy water infiltration is key for evaluating agrochemical groundwater migration. To this end, we designed and conducted an experiment with two aims: (1) to describe the water infiltration dynamic that occurs throughout the growing season and wet-dry cycling in rice paddies, and (2) to quantify the infiltration that takes place under two different water managements (continuous flooding (CF) and delayed submersion (DS)). The two-year field-scale study took place in Vercelli (Italy) during which the water balance in six rice paddies was monitored hourly and the infiltration rate dynamic was calculated for each wet-dry cycle.The average daily infiltration rate decreased between the first and second cycles, increased after the third cycle, and reached its maximum value at the growing season end. Water infiltrated during the first 40 h of each wet-dry cycle and particularly at the first and fourth wetting induced the highest groundwater pollution risk, with a larger potential in DS. Also, DS did not save water, as the total water used in the two treatments was identical.